The present invention relates to a compressor and particularly to an oil system for a compressor. More particularly, the present invention relates to an oil system for compressors in parallel or multiplexed applications.
Compressor racks, such as those employed in large supermarket applications, often encounter difficulty in controlling the oil level in a compressor. Thus, it is possible for compressors to overfill with oil. The over full condition occurs when oil returns through a common suction header to different size compressors. This happens regardless of the oil separator efficiency. The oil overfill condition may also take place if a compressor is off for several hours or more. This is the result of normal vapor movement through the compressors discharge valves. Compressors can fail if they are operated with too much oil in the crankcase.
Energy usage penalties are also associated with high oil levels in compressors. For example, compressors with oil levels only ⅜ of an inch over the recommended level can suffer a decrease in efficiency of about four percent. The efficiency decreases due to the elevated power consumption required to pump or agitate the additional quantity of oil. The efficiency loss of each compressor varies with the manufacturer and compressor model in addition to the amount of oil overfill. Maintaining an oil level that is not too high and not too low, regardless of whether a compressor is running or not, will likely increase efficiency and will reduce the likelihood of premature compressor failure.
Compressor oil systems also require a certain type and nature of lubricant to remain miscible with refrigerants commonly used in the industry today. Ester oil is typically used in supermarket compressors and has two main components: carboxylic acid and alcohol. These two components act as cleaning solvents that scrub the inside of the piping and components, thereby loosening abrasive particulate found in the refrigeration system. The suspended particulates precipitate the need for more frequent oil changes, which can be costly. An alternative to changing the oil is to change the compressor more often due to the abrasives in the lubricant. Further, it has been suggested that bearing life can be increased by decreasing the size of the particulates in the lubricant.